The term “E-DCH” refers to the Enhanced Dedicated Channel provided in wireless communication networks configured according to 3GPP UMTS standards—where “3GPP” refers to the Third Generation Partnership Project and “UMTS” denotes the Universal Mobile Telecommunications Service, as defined by the relevant 3GPP Technical Specifications.
The E-DCH is a transport uplink channel and, among other things, the E-DCH provides for random access transmissions by User Equipments, “UEs” operating in the CELL_FACH state. In particular, the network uses a pool of common E-DCH resources that can each be temporarily assigned to a UE in CELL_FACH state. In the current standard, there are up to 256 Radio Network Temporary Identifiers or “RNTIs” used for differentiating UEs making random accesses on the E-DCH within a cell, and a maximum of 32 random access preambles defining a maximum of 32 individual common E-DCH resources that can be allocated to respective individual UEs at any given time.
To transmit on a common E-DCH resource, a UE begins transmitting a random access preamble using a transmit power ramping. The NodeB—a base station in the UMTS vernacular—detects the random access preamble and allocates an available common E-DCH resource. The controlling NodeB—a UMTS base station—allocates individual ones of the common E-DCH resources to UEs attempting random access transmissions on the E-DCH, with the allocated resources subsequently being released back into the pool.
Data frames transmitted by UEs on common E-DCH resources are received at the supporting NodeB and passed along to the associated Radio Network Controller or “RNC”. Each UE uses Transmission Sequence Numbers, “TSNs”, to identify the sequence of data frames transmitted in each access of the common E-DCH resources. The RNC performs data re-ordering as needed based on the TSN of the data frames received from a given UE and it differentiates between the data frames received from different UEs based on the E-RNTI.
According to the 3GPP Technical Specification identified as TS 25.435 (see e.g. version 10.4.0), a UE that has been allocated a common E-DCH resource must reset its MAC-is when releasing that resource, and must also reset its TSN counter to zero for all logical channels mapped to the E-DCH. Here, the term “MAC-is” denotes one of the Medium Access Control entities within the UE that control access to the E-DCH. Accordingly, the UE resets its TSN counter for each access it makes on the common E-DCH resources in the CELL_FACH state, meaning that the TSN of the first MAC-is Protocol Data Unit, “PDU”, transmitted in any given access is set to zero and incremented for each successive data frame transmitted in that same access.
The NodeB of the involved cell controls the contention-based accesses of the common E-DCH resources in the cell. In particular, the NodeB assigns one of the common E-DCH resources to a given UE for a given random access by that UE. The allocated resource is subsequently released—either by the UE or based on expiry of an allocation timer—and thus becomes available for a subsequent random access by the same UE or any other UE operating in the cell.
There are several potential challenges arising from the above arrangement and operation. For example, TSN values range from 0 to 63, meaning that a UE transmitting more than sixty-four data frames within the same access will reuse one or more of the TSN values used for data reordering at the RNC. Further, while the RNC can distinguish between data frames from different UEs, based on the different E-RNTIs assigned to those UEs, the RNC cannot necessarily distinguish between the data frames sent from the same UE in two successive accesses.
As a particular example, a given UE is allocated common E-DCH resources for a given random access, referred to as a “first” access, those resources are released by the first UE upon completion of the first access, and the UE makes an immediate or almost immediate second random access on the common E-DCH resources. The E-RNTI seen by the RNC will be the same for the first and second accesses. Moreover, the TSN numbering will start at zero for the data frames received at the RNC for the first access and for those received for the second access.
Thus, because the RNC does not know when common E-DCH resources are allocated or released, it is recognized herein that there is a possibility of the RNC confusing data between successive random accesses by a UE on the common E-DCH resources. Particularly, data reordering at the RNC relies on use of a certain timer, wherein the RNC “waits” on a packet missing from an overall sequence of patents until expiry of a “T1” timer. Now, during the run time of the T1 timer, the UE associated with the missing packet might end its data transmission and release the involved common E-DCH resource. If that same UE makes a subsequent random access within the timing window of T1, the RNC may receive a data frame in the second access that has the same E-RNTI and TSN value of the data frame missing from the prior access.
For example, assume that a UE has sent ten data packets with TSNs of 0 to 9 and then releases the common E-DCH resource used for that access. Further, assume that the RNC has not received the TSN=4 data packet from that access. If the UE initiates another random access data transmission on the E-DCH, data transmissions for that subsequent access will start with TSN=0. If the UE sends five or more data packets, the RNC will see a data frame having TSN=4 from this subsequent access but will not be able to differentiate it from the TSN=4 data frame missing from the immediately prior access by the same UE. The result will be that the RNC mixed up data from two different data transmissions because it cannot distinguish between different accesses by the same UE.